Motor not getting water on startup

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I've got a I/O OMC 5L V8 with a Cobra outdrive. Had the issue with it not getting water when we first start it after launching. I can run it with ears with no problem. I've pulled a cooling line at start up and it doesn't start to pump water until I run the RPM's up. Just reaching out to see if there may be a simple fix for this before I take it in. Any and all suggestions and comments would be great.

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is your motor overheating at all?? i had an old mercruiser that i smoked the pump in. so i put a new impeller in it. it did pump water but the engine overheated. i ended up having to change the impeller housing and another new impeller, and that fixed it. just a thought. let us know what happens.

maby some of the other guys can help you. but it may be normal, i just dont know. but using the muffs you have pressure pushing the water up. and just sitting in the water it has to do all the pumping.

once you rev the engine and it starts pumping, does it keep pumping when you go back to idle?? if you shut it off do you have to rev the engine to get it pumping again??

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2 Weeks ago, I was at Erie and we launched the boat got it running and put it in a slip. I left it running in the slip while I went and put some rain gear on and got some things around. When I got back to the boat it was maxed on the temp gauge. Once it cooled I was able to get it running and get the water to start pumping again. Never had another problem the rest of the weekend. Sunday was the first I had run it(other than with muffs) since coming back from Erie. Started it and the temp started climbing again. Shut it down and as I said originally above, pulled the cooling line to check for water flow. Didn't get it till I rev it. When I go back to an idle it still pumps, I managed to troll all afternoon Sunday with no issues. It still pumps after shutting off and back on. Just seems it needs a little persuasion to first get primed.

Larry-I did check to see if all the fins were running the correct direction.

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if you pulled the water line coming from the outdrive to the engine and wasnt getting water then its not your thermostat. i would check the water intakes real good to make sure something isnt blocking the water. sometimes bees will build nests in places like that. if i didnt find anything i would go ahead and invest in a new pump and housing kit. all i changed on mine when i had the overheating problem was the bottom wear plate the impeller and the upper housing.

i dont know if you know how to change the waterpump yourself. but on a mercruiser it is quite simple. but you can google changing a waterpump on cobra outdrive. you will get plenty of info. i could give you step by step for a mercruiser or mercury outdrive. but thats the only thing i know about. it takes me about 1 hour to change the pump. but now i have to have help to lift the outdrive back up. i have changed plenty of them by myself in the good old days,LOL.

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I appreciate the help Sherman. I'm still not for sure whats going on. My brother had the boat out Tuesday and didn't have any problems at all. It seems to be a random thing, usually happens when the boat sits for a week or so.

I've done mercruiser pumps before and they are pretty simple like you said. The cobra makes the mercruiser seem like a lot of work. All you do is pull a simple cover plate and its right there, no dropping the lower unit. I'm thinking I'm going to change my thermostat out. I'm not for sure that's the problem, but I know it is something that I haven't replaced since I bought the boat. I'll at least eliminate the possibility.

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I appreciate the help Sherman. I'm still not for sure whats going on. My brother had the boat out Tuesday and didn't have any problems at all. It seems to be a random thing, usually happens when the boat sits for a week or so.

I've done mercruiser pumps before and they are pretty simple like you said. The cobra makes the mercruiser seem like a lot of work. All you do is pull a simple cover plate and its right there, no dropping the lower unit. I'm thinking I'm going to change my thermostat out. I'm not for sure that's the problem, but I know it is something that I haven't replaced since I bought the boat. I'll at least eliminate the possibility.

Thanks again to everyone.

if its that simple to change your waterpump. i would go ahead and change it out also. if it wasnt getting water for whatever reason that time it overheated at the dock, it could have damaged the pump. it would just eliminate one other thing that could be the problem.

i have a friend who i met on another forum. he had just put a new pump in his year before last. then last year he had a problem all summer long. he even took the thermostat out of his boat. nothing he did helped. he took it to a good friend of his that works on boats. the first thing he did was check the impeller. it had 2 blades that were missing part of them. he replaced the impeller this spring. he said it was doing good. so he put the thermostat back in. it was running to cool.LOL.